C-Methionine PET/CT in Central Nervous System Tumours: A Review

A.   M.   Maffione; C.      Nanni; V.      Ambrosini; S.      Trespidi; E.      Lopci; V.      Allegri; P.      Castellucci; G.      Montini; S.      Boschi; S.      Fanti

Abstract

Central nervous system (CNS) malignant tumors are usually treated with different combinations of surgery, radiotherapy and chemotherapy to achieve a radical treatment. After therapy, conventional imaging procedures (CT and MR) are useful to detect disease relapse but a correct differential diagnosis in presence post-surgical fibrosis, radionecrosis or oedema (benign conditions) may sometime be difficult. CNS shows physiologically an intense uptake of FDG and consequently, small and/or hypo/isometabolic malignant lesions are very difficult to detect, as they may be masked by the hypermetabolic surrounding tissue. 11C-Methionine is a radiolabeled aminoacid that physiologically do not accumulate into the brain, nor in case of benign conditions such as fibrosis, necrosis or oedema. On the other side, malignant lesions (although low grade) present an increased 11C-Methionine uptake due to an increased proteic metabolism and vascular permeability. Therefore 11CMethionine has optimal tumor-to-background ratio, making this radiotracer very useful to study CNS malignant tumors. The most appropriate indication for 11C-Methionine PET is the presence of non conclusive conventional imaging procedures, not allowing to discriminate between benign conditions and disease relapse. Other applications of 11C-Methionine PET are the definition of the radiotherapy field, the localization of the most metabolic area inside a mass to guide the biopsy and the early evaluation of radiotherapy effect, but all these applications are marginal and not yet validated.

Keywords: 11C-Methionine, PET/CT, brain cancer imaging, central nervous system

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